1. Field of the Invention
The present invention relates mainly to a motor employed in office automation instruments.
2. Description of the Prior Art
Fixedly mounted on a spindle of a conventional motor is an inner race of a ball bearing which is constructed of: an outer race; the inner race disposed inside the outer race; and, a plurality of balls disposed between the outer race and the inner race. The inner race mounted on the spindle of the motor is generally fixed thereto by the use of a suitable adhesive, as follows:
(a) As shown in FIG. 5(a), an annular groove, which is formed between a chamfered outer end portion of the spindle and a corresponding chamfered inner end portion of the inner race of the ball bearing to assume a V-shaped form in cross section, is filled with the adhesive which is permitted to flow into an annular clearance formed between an outer peripheral surface of the spindle and an inner peripheral surface of the inner race of the ball hearing and be cured therein so as to fix the inner race of the ball bearing to the spindle of the motor.
However, this first approach is not adequate, because the adhesive filled the annular groove does not sufficiently flow into the annular clearance formed between the spindle and the inner race of the ball thus provides a poor adhesive bond therebetween.
(b) As shown in FIG. 5(b), a small-diameter portion is formed in an end portion of the spindle to form a relatively large annular clearance between the outer peripheral surface of the small-diameter portion of the spindle and the inner peripheral surface of the inner race of the ball bearing. Then, the adhesive filled in the end annular groove assuming the V-shaped form in cross section is permitted to flow into such relatively large annular clearance and be cured therein so as to fix the inner race of the ball bearing to the spindle of the motor.
Consequently, in the motor of a normal size, this second approach is adequate, because the annular clearance formed between the inner race and the spindle can be sufficiently filled with the adhesive to provide a good adhesive bond therebetween.
In this second approach, however, when the adhesive is applied to an inner race of a miniature ball bearing mounted on a spindle to a miniature motor, the inner race of the miniature motor is deformed when the adhesive is cured. Consequently, the second approach is not adequate in case of the miniature motor.